Many remote accessory devices are designed to be powered by mobile direct current (D.C.) sources such as storage batteries and related systems used in automobiles, pleasure boats, etc. These devices are often powered by electric current drawn from a cigarette lighter receptacle. In order to draw current from the lighter receptacle, an adapter must be provided to interface both mechanically and electrically with the lighter receptacle. Such apparatus can exist in a variety of configurations. For example, one end of a conductive cable may be hard-wired into the remote electrical device and the other end adapted to be plugged directly into the lighter receptacle. Alternatively, the remote end of the cable may be provided with a disconnecting plug. Examples of devices which may be thus powered include portable spot-lights, car phones, compact disc players, air compressors and thermoelectric coolers.
The power needs of accessory devices vary. Given the wide array of devices in use, it is certain that the power needs of some devices will exceed the capability of many adapters. For example, a lighter adapter designed to power a car phone will not ordinarily carry sufficient current for high powered devices such as thermoelectric devices. Power needs may vary in other respects as well. For example, a thermoelectric device may operate in either a heating mode or a cooling mode, depending on the polarity of the current supplied to the device. Since the polarity of the current available at the lighter receptacle is fixed, and since existing lighter adapters cannot change the polarity, a polarity switch must be incorporated into the accessory employing the thermoelectric device. Such a switch adds to the weight, complexity and cost of the device.